1. Field of the Invention:
The present invention relates to a resin bonded type magnet and its manufacture, more particularly, relates to a magnet prevented from deterioration caused by oxidation and by corrosion during use and its manufacturing method.
2. Description of Prior Art:
An alloy magnet (hereinafter called a rare earth magnet) comprising a rare earth metal and a transition metal as the main ingredient is possessed of excellent magnetic properties compared with a conventional ferrite type or an Alnico type magnet, and therefore, it has been recently utilized in various fields. However, it can be easily oxidized, and the defects are remarkably observed in a Nd-Fe-B type magnet, in particular. A magnet comprising such rare earth magnetic powder bonded with a synthetic resin binder gives rise to elapsing deterioration of magnetic properties due to oxidation and corrosion under humid atmosphere in service environment.
In order to overcome these problems, a method to coat the above magnet with an acrylic resin or an epoxy resin is proposed in Japanese Non-examined Publication No. 63-244711 and No. 63-244710. However, though some effects against deterioration due to oxidation and corrosion are recognizable using the above method, practical satisfaction is not fully obtained. In other words, the above conventional technology cannot provide practically satisfactory corrosion resistance to such a magnet owing to the following reasons;
(1) Though a resin layer suppresses to some extent the arrival of oxidizable and corrosive substances such as oxygen to the magnetic surfaces, there are no suppression effects against growth of oxidized and corroded products. PA0 (2) Satisfactory adhesion between a magnet and a resin cannot be obtained.